The deeper layers of the superior colliculus receive convergent multimodal sensory input and are involved in orienting movements of the eyes, head and ears to sensory targets. Yet because the coordinate systems of its various inputs differ (e.g., retinocentric visual input vs. head-centered auditory input), it is not clear how they are combined and translated into accurate motor outputs. The specific aims of this project focus on: 1. Coordinates of auditory signals. a. Do auditory/visual neurons carry a signal of initial oculomotor error (i.e., the difference between target position and eye position before a saccade is made to the target)? These tests will be conducted in head-fixed animals. b. Do different cells signal gaze motor error? These tests will be done in head-free animals. c. Do visual/auditory interactions between targets at different sites depend on the oculomotor error of the auditory target relative to that of the visual target rather than on their retinocentric or head-centered coordinates? 2. Signals related to impending movements of the head, eye and gaze. a. Do some tectal neurons signal gaze motor error when gaze saccades are made to auditory targets, regardless of whether the head is fixed or is free to move? b. Does the vector of stimulation-elicited eye saccades depend on the type of movement-related cells in the immediate vicinity of the stimulating electrode? c. Does the discharge of two types of saccade-related neurons (saccade-related burst neurons and long-lead neurons) depend on the velocity of saccadic eye movements as well as their amplitude and duration? 3. Signals related to impending pinnae movements and their influence on the location of auditory receptive fields. a. Are orienting movements of the pinnae so closely linked to those of the eyes and head that the shifts in location of auditory receptive fields with eye position, previously reported, depend partially on the correlated movements of the pinnae? b. Do SC neurons show phasic discharge before movements of the pinnae even if no head or eye movements occur? The method to be used for these studies is extra-cellular recording of single units in behaving animals. These studies are potentially relevant to the understanding of a wide variety of neurological disorders which involve control of the extraocular and neck muscles as well as to the basic understanding of important theoretical issues of how sensory signals are transformed into motor coordinate systems.